Pain that is well managed during and immediately after surgery improves the health of patients (by decreasing physiologic stress) and the potential for chronic pain. Therefore, acute pain management is an integral part of any anaesthetic. Acute pain management can be pre-emptive (where pain medication is given prior the patient waking from an anaesthetic or before pain starts after surgery) or responsive (where pain medication is given in response to pain perception).

Many strategies are effective in acute pain management including epidural infusions, opioid drugs, non-steroidal anti-inflammatory drugs and patient-controlled analgesia. Nociception (pain sensation) is not hard-wired into the body. Instead, it is a dynamic process where persist painful stimuli can sensitive the system and either make pain management difficult or chronic pain develop. For this reason, pre-emptive acute pain management may reduce both acute and chronic pain. However pain management needs to be tailored to the surgery, the environment (in-patient/out-patient) and the individual patient.

Most healthy people don't have any problems with general anaesthesia. Although many people may have mild, temporary symptoms, general anaesthesia itself is exceptionally safe, even for the sickest patients. The risk of long-term complications, much less death, is very small. In general, the risk of complications is more closely related to the type of procedure you're undergoing, and your general physical health, than to the anaesthesia itself.

Some of the factors that can increase your risk of complications include:

Risks and complications as they relate to anaesthesia are classified as either morbidity (a disease or disorder that results from anaesthesia) or mortality (death that results from anaesthesia). Attempting to quantify how anaesthesia contributes to morbidity and mortality can be difficult because a person's health prior to surgery and the complexity of the surgical procedure can also contribute to the risks.

Prior to anaesthetic in the early 19th century, the physiologic stress from surgery caused significant complications and many deaths. The faster the surgery was, the lower the rate of complication (leading to famous reports of 30 second amputations). The advent of anesthesia, allowed more complicated and life-saving surgery to be completed, decreased the physiologic stress of the surgery but added an element of risk. It was 2 years after the introduction of ether anaesthetics that the first death, directly related to the anaesthetic was reported.

Morbidity can be major (myocardial infarction, pneumonia, pulmonary embolism, renal failure/insufficiency, postoperative cognitive dysfunction, allergy or minor (minor nausea, vomiting, readmission). There is usually overlap in the contributing factors that lead to morbidity and mortality between the health of the patient, the surgery being performed and the anaesthetic. Estimates vary, but about 1 or 2 people in every 1,000 may wake up briefly while receiving general anaesthesia. The person usually doesn't feel pain, but is aware of his or her surroundings.

In very rare situations, some people experience excruciating pain in spite of general anaesthesia. In this situation, because of muscle relaxants given prior to surgery, people aren't able to move or speak or make others aware of their distress. This could be due to the fact that some people are resistant to the anaesthetic agents used. It is important to minimize pain and any discomfort before and during the operation in order to minimize stress on the body and mind, which may lead to long-term psychological problems, similar to post-traumatic stress disorder. In order to prevent this, the patient needs to disclose any effects previous anaesthesia had on them. 

The following factors appear to make this phenomenon — also called unintended intraoperative awareness — more likely: